Last week, there were so many of the mock arguments that lawyers call moot courts that they threatened to exhaust something that had never been thought in short supply: Washington lawyers willing to pretend to be Supreme Court justices.

The problem, said Paul D. Clement, who represents the 26 states challenging the law, was not just the length of the arguments the court will hear, but the variety of topics to be addressed.

The law itself is a sprawling revision of the health care system meant to provide coverage to tens of millions of previously uninsured Americans by imposing new requirements on states, employers and insurance companies and, through what has been called the individual mandate, by requiring most Americans to obtain insurance or pay a penalty.

The decision in the case will have enormous practical consequences for how health care is delivered in the United States. It is likely to land in June, with large repercussions for both Mr. Obama and his Republican challenger just before the two parties hold their nominating conventions.

The justices have broken the case into four discrete issues, scheduling a separate session for each, for a total of six hours, the most in one case in more than 40 years. Mr. Clement, like his principal adversary, Solicitor General Donald B. Verrilli Jr., will be arguing three times.

Walter Dellinger, who was acting solicitor general in the Clinton administration, said he was worried about “the enormous endurance challenge this will be for Verrilli and Clement.” Mr. Dellinger, who has argued more than 20 cases in the Supreme Court, said making even a single 30-minute presentation is draining.

“The day or two after a Supreme Court argument, I just basically collapse,” Mr. Dellinger said.

The central issue in the case, to be argued for two hours on Tuesday, is whether the individual mandate is constitutional.

But first, on Monday, the justices will hear 90 minutes of arguments from three lawyers about whether they should be hearing the case at all.

But neither the Obama administration nor the parties challenging the law agree with that ruling. So the court appointed a Washington lawyer, Robert A. Long, to speak on behalf of that argument. The court makes such appointments every year or so, and the practice has been the subject of some skeptical academic commentary.

Mr. Long will be followed on Monday by Mr. Verrilli and a lawyer for the private challengers, Gregory G. Katsas.

The Obama administration initially agreed that the court could not rule on challenges to the law for a few more years, but it reversed course in the appeals courts. It has since relinquished other opportunities to slow down the case and insists it wants a prompt decision.

Mr. Long was one of three lawyers who presented mock arguments in the grand ceremonial courtroom at the Supreme Court Institute at the Georgetown University Law Center. On other days, the moot court program there helped prepare Mr. Clement, twice, as well as Michael A. Carvin, who represents private challengers to the law.

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Abortion opponents laid flowers at the Supreme Court for the potential lives lost every day.Credit
Doug Mills/The New York Times

Mr. Clement and Mr. Carvin will face Mr. Verrilli on Tuesday for the main event, the argument over whether the requirement to obtain insurance was authorized by the Constitution as a regulation of interstate commerce or by the power to levy taxes. The administration says the health care law is well within the powers granted by the Constitution, while the challengers say it plainly exceeds what the federal government may do.

For Wednesday, the court has scheduled a double feature.

In the morning, the justices will hear 90 minutes of arguments about what should happen if they strike down the mandate. The federal appeals court in Atlanta, whose decision is under review, ruled that it was possible to remove just the mandate and leave the balance of the law intact.

As with the 1867 law, neither side agrees with that ruling. So here, too, the court has appointed an outside lawyer, H. Bartow Farr III, to argue the point.

Mr. Clement will contend that the entire law must fall. A colleague of Mr. Verrilli’s in the solicitor general’s office, Edwin S. Kneedler, will argue for a middle ground, saying that most of the law should stand but that two other provisions — one forbidding insurers to turn away applicants, the other barring them from taking account of pre-existing conditions — are intertwined with the mandate and would have to fall along with it.

On Wednesday afternoon, the two main lawyers, Mr. Verrilli and Mr. Clement, will return for a one-hour encore, this time to argue over whether Congress exceeded its constitutional authority in expanding the eligibility and coverage thresholds that states must adopt to remain eligible for Medicaid, the federal-state program that provides health care to poor and disabled people.

There is room for only about 400 people in the courtroom, and prominent lawyers and politicians have been scrambling for tickets. The court has set aside about 60 seats for members of the public, and the line started forming on Friday morning.

When he started thinking about how to prepare, Mr. Clement said, “You had to make a decision about whether this is one argument or three arguments,” referring to the individual mandate, what other parts of the law should fall if it is struck down, and the Medicaid expansion. He decided that it was three separate arguments, largely because the justices seemed to think so.

Mr. Clement, who has argued more than 50 times in the Supreme Court, said he usually scheduled two moot courts per argument. Here, he said, he settled for five sessions for three arguments, one on every weekday last week — two at Georgetown, two at the National Association of Attorneys General and one at the U.S. Chamber of Commerce.

Lawyers in the solicitor general’s office also hold moot courts, though in a less grand setting.

“It’s just the lunchroom, basically,” said Neal K. Katyal, who was the acting solicitor general until last summer and who defended the health care law in federal appeals courts. “There is probably not a room in Washington that looks less like the United States Supreme Court.”

There are two main points to the exercise, said Mr. Katsas, who will argue on behalf of the private challengers that the court should not wait until 2015 to rule.

“One is identifying difficult and likely questions,” he said, “and the other is just practicing articulating the answers in the stress of something that approximates being at the podium.”

Mr. Clement said he valued the diversity among the pretend justices. “Some of the most helpful questions I’ve gotten were from people I’d guess are rooting against me,” he said. “Most helpful,” he explained, meant “the most thought-provoking, most difficult, most challenging.”

Irving L. Gornstein, the executive director of the Georgetown program, which holds moot courts in a vast majority of Supreme Court cases, said the sessions were helpful not only for the advocates but also for students, who are allowed to attend if they promise to keep what they see and hear confidential.

Supreme Court advocates can be obsessive, and many say there is no such thing as too much preparation. Mr. Katyal said he used to download recordings of his moot courts to his iPod.

“I would jog,” Mr. Katyal said, “and listen to my moots and listen to how I sounded.”

Emmarie Huetteman contributed reporting.

A version of this article appears in print on March 26, 2012, on page A1 of the New York edition with the headline: 3-Day Marathon Awaits Lawyers In Health Case. Order Reprints|Today's Paper|Subscribe